Improve the Light transport in game engines documentation (#2742)

This also fixes a Sphinx build warning caused by `_scene referred_`.
Using `*` for italics solves the issue.

tutorials/3d/high_dynamic_range.rst

@@ -21,11 +21,11 @@ their respective scenes. So what's the problem?
 The display has a limited range of intensity, depending on the display type.
 The game engine renders to an unlimited range of intensity values, however.
 While "maximum intensity" means something to an sRGB display, it has no bearing
-in the game engine; there is only a potentially infinitely wide range of intensity
-values generated per frame of rendering.
+in the game engine; there is only a potentially infinitely wide range
+of intensity values generated per frame of rendering.
 
 This means that some transformation of the scene light intensity, also known
-as scene-referred light ratios, need to be transformed and mapped to fit
+as *scene-referred* light ratios, need to be transformed and mapped to fit
 within the particular output range of the chosen display. This can be most
 easily understood if we consider virtually photographing our game engine scene
 through a virtual camera. Here, our virtual camera would apply a particular
@@ -42,71 +42,69 @@ the ratios out of the uniquely colored lights at each reddish, greenish,
 and blueish emission site.
 
 For a majority of computer displays, the specifications of the display are
-outlined in accordance with IEC 61966-2-1, also known as the 1996 sRGB specification.
-This specification outlines how an sRGB display is to behave, including the
-color of the lights in the LED pixels as well as the transfer characteristics
-of the input (OETF) and output (EOTF).
+outlined in accordance with IEC 61966-2-1, also known as the
+1996 sRGB specification. This specification outlines how an sRGB display
+is to behave, including the color of the lights in the LED pixels as well as
+the transfer characteristics of the input (OETF) and output (EOTF).
 
-Not all displays use the same OETF and EOTF as a computer display however,
-for example, television broadcast displays use the BT.1886 EOTF. It should
-be noted that Godot is limited in its pixel management chain,
-and only supports sRGB displays currently.
+Not all displays use the same OETF and EOTF as a computer display.
+For example, television broadcast displays use the BT.1886 EOTF.
+However, Godot currently only supports sRGB displays.
 
 The sRGB standard is based around the nonlinear relationship between the current
 to light output of common desktop computing CRT displays.
 
 .. image:: img/hdr_gamma.png
 
-The mathematics of a scene referred model require that we multiply the scene by different
-values to adjust the intensities and exposure to different light ranges.
-The transfer function of the display cannot appropriately render
+The mathematics of a scene-referred model require that we multiply the scene by
+different values to adjust the intensities and exposure to different
+light ranges. The transfer function of the display can't appropriately render
 the wider dynamic range of the game engine's scene output using the simple
-transfer function of the display however, and therefore a more complex approach
-to encoding is required.
+transfer function of the display. A more complex approach to encoding
+is required.
 
 Scene linear & asset pipelines
 ------------------------------
 
-Working in scene linear sRGB is not as simple as just pressing a switch. First,
+Working in scene-linear sRGB is not as simple as just pressing a switch. First,
 imported image assets must be converted to linear light ratios on import. Even
-when linearized, those assets may not be perfectly well suited for use as textures,
-depending on how they were generated.
+when linearized, those assets may not be perfectly well suited for use
+as textures, depending on how they were generated.
 
 There are two ways to do this:
 
 sRGB transfer function to display linear ratios on image import
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This is the easiest, but not the most ideal, method of using sRGB assets.
-One issue with this is loss of quality. Using 8 bit per channel to represent
-linear light ratios is not a sufficient but depth to quantise the values correctly.
-These textures might later be compressed too, which can exacerbate the problem.
+This is the easiest method of using sRGB assets, but it's not the most ideal.
+One issue with this is loss of quality. Using 8 bits per channel to represent
+linear light ratios is not sufficient to quantize the values correctly.
+These textures may also be compressed later, which can exacerbate the problem.
 
 Hardware sRGB transfer function to display linear conversion
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The GPU will do the conversion after reading the
-texel using floating point. This works fine on PC and consoles, but most
-mobile devices do no support it, or do not support it on compressed
-texture format (iOS for example).
+The GPU will do the conversion after reading the texel using floating point.
+This works fine on PC and consoles, but most mobile devices don't support it,
+or they don't support it on compressed texture formats (iOS for example).
 
 Scene linear to display referred nonlinear
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 After all the rendering is done, the scene linear render requires transforming
-to a suitable output such as an sRGB display. To do this, enable sRGB conversion in the
-current :ref:`Environment <class_Environment>` (more on that below).
+to a suitable output such as an sRGB display. To do this, enable sRGB conversion
+in the current :ref:`Environment <class_Environment>` (more on that below).
 
-Keep in mind that sRGB -> Display Linear and Display Linear -> sRGB conversions
-must always be **both** enabled. Failing to enable one of them will
+Keep in mind that the **sRGB -> Display Linear** and **Display Linear -> sRGB**
+conversions must always be **both** enabled. Failing to enable one of them will
 result in horrible visuals suitable only for avant-garde experimental
 indie games.
 
 Parameters of HDR
 -----------------
 
-HDR setting can be found in the :ref:`Environment <class_Environment>`
-resource. These are found most of the time inside a
+HDR settings can be found in the :ref:`Environment <class_Environment>`
+resource. Most of the time, these are found inside a
 :ref:`WorldEnvironment <class_WorldEnvironment>`
-node or set in a camera. For more information see
+node or set in a Camera node. For more information, see
 :ref:`doc_environment_and_post_processing`.